Glitches

Infinite Money

First of all, you need to raise the Barter skill to level 10. Once this has been achieved, the following items can be sold for more money than it costs to buy them: Health Potion, Mana Potion, Town Portal Scroll & Identify Scroll. Simply purchase as many of these as possible (holding down the 'X' button helps on the X360 version) and sell them back to the shop for a ~20% profit. This can be repeated as many times as necessary.
Important note: This trick does not work for the larger Health and Mana Potions, only the regular ones.

Infinite Potions

Create a new character. Once you're in town, place all your character's potions (including your Respec Potion if you have one) into the shared stash chest on the north side of Torchlight. You can now delete this character. Load another character, and you can pick up the potions your deleted character left in the chest. You can do this as many times as desired.

Item Cloning Trick (Pre-Patch)

When in the town of Torchlight, open the pause menu and return to the title screen to save the game. Reload the same file and then place any items you wish to clone in the shared stash. Now sign out of Xbox Live: This will return you to the title screen (the same effect will be achieved if you return to the Xbox dashboard or turn off your console). Sign in again and reload your file and any items you stashed will also exist in your inventory!